Many applications utilize gases that have been generated from liquid sources. Vaporization devices have been designed to vaporize liquids and release the resulting vapor under pressure. In applications in which a pressurized vapor stream is desired, prior art devices generally require that liquid be supplied to the device under pressure, or the vapor is otherwise pressurized by external means. For example, in a pressurized boiler system, the liquid is generally required to be supplied under at least as much pressure as that of the produced vapor. Pressurized liquid sources are usually inconvenient to use, heavy to transport, potentially explosive, and prone to leakage. It would be desirable, for many applications, to produce a pressurized vapor stream from a liquid at ambient pressure, or at a relatively low pressure.
In most liquid fuel vaporization applications, liquid fuel is vaporized, then mixed with air or an oxygen-containing gas, and the vaporized fuel/gas mixture is ignited and burned. The liquid fuel is generally supplied under pressure, and atomized by mechanical means or heated to vaporization temperatures using an external energy source. It would be desirable, for combustion applications in particular, to produce a pressurized vapor stream from a liquid fuel provided at ambient, or relatively low, pressure.
Portable burners and light sources that utilize liquid fuels generate liquid fuel vapor, which is then mixed with air and combusted. Combustion devices that burn fuels that are liquids at atmospheric temperatures and pressures, such as gasoline, diesel fuel and kerosene, generally require the liquid fuel to be pressurized by a pump or other device to provide vaporized fuel under pressure. Fuels such as propane and butane, which are gases at atmospheric pressures but liquids at elevated pressures, can also be used in portable burners and light sources. Storage of these fuels in a liquid form necessitates the use of pressurized fuel canisters that are inconvenient to use and transport, are frequently heavy, may be explosion hazards, require expensive valves which are prone to leaking, and are facing increasing regulatory pressure and disposal costs.
The fuel boiler of propane and butane burners is the reservoir or storage tank itself, from which the gases are released under pressure as vapor. When vapor is withdrawn from the fuel reservoir, the pressurized reservoir acts as a boiler, and draws the required heat of vaporization from ambient air outside the tank. These systems have many disadvantages. The vapor pressure of propane inconveniently depends upon ambient temperature, and the vapor pressure is generally higher than that needed for satisfactory combustion in a burner. While butane fuel has an advantageous lower vapor pressure than propane, burners using butane have difficulty producing sufficient vapor pressure at low ambient temperatures. Burners using a mixture of propane and butane fuel provided under pressure in disposable canisters have also been developed. This fuel mixture performs well at high altitudes, but still does not perform well at low ambient temperatures.
A needle valve can be used to control propane vapor at tank pressure to regulate the fuel flow, and thus the heat output, of a burner. Burner control using a needle valve tends to be delicate and sensitive to ambient temperatures. Alternatively, a pressure regulator can be used to generate a constant and less hazardous pressure of propane that is independent of tank temperature. Propane pressure regulators are commonly used in outdoor grills, appliances for recreational vehicles and boats, and domestic propane installations. Unfortunately, regulators are bulky and are seldom practical for application to small-scale portable burner devices.
Despite considerable development efforts and the high market demand for burners for use in stoves, lamps and the like, that operate safely and reliably under a wide variety of ambient temperature, pressure and weather conditions, commercially available combustion devices are generally unsatisfactory.
Wicking systems that use capillary action to convey and vaporize liquid fuels at atmospheric pressure are known for use in liquid fuel burners. U.S. Pat. No. 3,262,290, for example, discloses a liquid fuel burner in which a wick stone is fastened in a fuel storage container and feeds liquid fuel from the fuel reservoir to the burner. In this system, liquid fuel is provided to the wick stone by an absorbent textile wick, and the wick stone is biased against a burner wick.
U.S. Pat. No. 4,365,952 discloses a liquid fuel burner in which liquid fuel is drawn up from a reservoir by a porous member having a fuel receiving section and a fuel evaporation section. Liquid fuel is supplied by capillary action at a rate matching the rate of evaporation of the fuel. Air is supplied to the fuel evaporation section, and liquid fuel is evaporated from the surface at a rate corresponding to the rate of air supply. The gaseous fuel and air is mixed and jetted from a flame section to a burning section. An externally powered heater maintains the porous member of the fuel evaporation section substantially at a constant temperature irrespective of the rate of evaporation of the liquid fuel.
U.S. Pat. No. 4,421,477 discloses a combustion wick comprising a fuel absorption and a fuel gasifying portion designed to reduce the formation and deposition of tar-like substances in the wick. The wick comprises silica-alumina ceramic fibers molded with an organic binder, with part of the wick provided with a coating of an inorganic pigment, silicic anhydride and a surface active agent. The wick may have a capillary pore size of about 1 to 50 microns, with smaller pore size wicks being less prone to accumulation of tar-like substances on the inside.
U.S. Pat. No. 4,465,458 discloses a liquid fuel combustion system in which the liquid fuel is drawn into a porous fiber material or fabric, which is intimately contacted by an externally powered heat generating member to evaporate and vaporize the liquid fuel. Air is introduced to promote vaporization of the liquid fuel and provide an admixed liquid/fuel mixture for burning. Combustion is variable by adjusting the heat input and the air supply.
U.S. Pat. No. 4,318,689 discloses a burner system in which liquid fuel is pumped into a cylindrical chamber having a porous sidewall. As a result of the pressure differential, the liquid fuel penetrates the porous wall to form a film on the external surface of the porous chamber wall. Preheated combustion air entrains and vaporizes the liquid fuel film formed on the external wall of the chamber, and circulates the fuel/air mixture to a combustion chamber. A portion of the hot exhaust or combustion gases may be returned for countercurrent heat exchange to preheat the combustion air.
U.S. Pat. Nos. 5,692,095, 5,870,525, 6,162,046, 6,347,936, 6,585,509 and 6,634,864 are incorporated by reference herein in their entireties and relate to predecessor capillary pump modules and systems having a capillary member for vaporizing and pressurizing liquids in a porous material. The capillary member has low thermal conductivity and small-sized pores that permit liquid to travel by capillary action toward the vaporization zone. The modules include an orifice plate having one or more orifices permitting the release of pressurized vapor and a sealing member forming at least a partial enclosure of the module, allowing vapor to accumulate and pressure to increase within the module.
The present invention contemplates further developments of and improvements to these types of capillary pumps. Specifically, the present invention involves the application of new materials combinations, new device architectures and methods of construction, and incorporation of entirely new features previously unanticipated. These improvements provide capillary pumps having substantially reduced manufacturing costs, increased performance, expanded ranges of utility in terms practical size, output, and substances that can be vaporized, as well as new functionality not achievable by the prior art.